The synthesis of two novel fused thienopyridopyridazines

Two previously unknown thienopyridopyridazine ring systems, thieno2′,3′:5,6]pyrido2,3-d]pyridazine-5,8,9(4H,6H,7H)-trione ( 4 ) and thieno3′,2′:5,6]pyrido2,3-d]pyridazine-4,5,8(6H,7H,9H)-trione ( 10 ) were synthesized and their chlorination reactions with phosphorus oxychloride were investigated.